The present invention relates to a process for producing a drawn wire, made of stainless steel, in particular a wire for reinforcing tires, having a diameter of less than 0.3 mm, by drawing a steel having a suitable composition and a suitable quality in terms of inclusions. The wire obtained by the process can be used in the field of the production of components subjected to fatigue.
Metal wire for reinforcing the elastomers in tires must have a small diameter, generally between 0.1 mm and 0.3 mm, and high mechanical properties. The tensile strength may be greater than 2300 MPa, the residual ductility, measured by the reduction in cross section in tension or torsion or by a wrap-around test, must be non-zero and the fatigue endurance limit, in rotary or alternating flexure, must be greater than 1000 MPa.
These characteristics are necessary for withstanding the static and alternating loads to which the wire is subjected in the assemblies incorporated into tires.
Furthermore, the drawing of stainless steel wire down to a diameter of between 0.1 and 0.3 mm must be possible under industrial conditions, i.e. with breakage frequencies as low as possible, while limiting the expensive operations such as heat treatments and intermediate annealing steps.
It is known, for reinforcing tires, to use a stainless steel wire in the highly strain-hardened state resulting from the drawing process.
Patent Application FR 9 312 528 relates to the use of a stainless steel wire having a diameter of between 0.05 mm and 0.5 mm, the tensile strength Rm of which is greater than 2000 MPa. The steel of which the wire is composed contains, in its composition, at least 50% of martensite obtained by drawing with a reduction ratio of greater than 2.11 and with intermediate annealing operations, the sum of the nickel and chromium contents being between 20% and 35%.
The subject of the invention is the production of a drawn wire, in particular a wire for reinforcing tires, having a diameter of less than 0.3 mm by drawing a base wire rod having a diameter of greater than or equal to 5 mm or a predrawn base wire made of steel of a given composition, the simplified production process ensuring, on the one hand, that the quality in terms of inclusions results in fewer breakages during drawing and, on the other hand, that the mechanical properties are improved.
The subject of the invention is a process for producing a drawn wire by drawing a base wire of stainless steel with the following composition by weight:
carbonxe2x89xa640xc3x9710xe2x88x923%
nitrogenxe2x89xa640xc3x9710xe2x88x923%,
the carbon and nitrogen satisfying the relationship C+Nxe2x89xa650xc3x9710xe2x88x923%,
0.2%xe2x89xa6siliconxe2x89xa61.0%,
0.2%xe2x89xa6manganesexe2x89xa65%,
9%xe2x89xa6nickelxe2x89xa612%,
15%xe2x89xa6chromiumxe2x89xa620%,
1.5%xe2x89xa6copperxe2x89xa64%,
sulfurxe2x89xa610xc3x9710xe2x88x923%,
phosphorus less than 0.050%,
40xc3x9710xe2x88x924%xe2x89xa6total oxygenxe2x89xa6120xc3x9710xe2x88x924%,
0.1xc3x9710xe2x88x924%xe2x89xa6aluminumxe2x89xa620xc3x9710xe2x88x924%,
magnesiumxe2x89xa65xc3x9710xe2x88x924%,
0.1xc3x9710xe2x88x924%xe2x89xa6calciumxe2x89xa65xc3x9710xe2x88x924%,
titaniumxe2x89xa650xc3x9710xe2x88x924%,
impurities inherent in the manufacture,
in which steel the inclusions of oxides have, in the form of a glassy mixture, the following proportions by weight:
30%xe2x89xa6SiO2xe2x89xa665%,
5%xe2x89xa6MnOxe2x89xa640%,
1%xe2x89xa6CaOxe2x89xa630%,
0%xe2x89xa6MgOxe2x89xa610%,
3%xe2x89xa6Al2O3xe2x89xa625%,
0%xe2x89xa6Cr2O3xe2x89xa610%,
the composition satisfying the following relationships:
when Si Mn less than 2%;
IM=551xe2x88x92462*(C %+N %)xe2x88x929.2*Si %xe2x88x928.1*Mn %xe2x88x9213.7*Cr %xe2x88x9229*(Ni %+Cu %)xe2x88x9218.5*Mo %, with
150xc2x0 C. less than IM less than xe2x88x9255xc2x0 C., and when
Si Mnxe2x89xa72%;
JM=551xe2x88x92462*(C %+N %)xe2x88x929.2*Si %xe2x88x9220*Mn %xe2x88x9213.7*Cr %xe2x88x9229*(Ni %+Cu %)xe2x88x9218.5*Mo %, with
xe2x88x92120xc2x0 C. less than JM less than xe2x88x9255xc2x0 C.,
which base wire undergoes drawing satisfying the following drawing conditions:
a cumulative deformation ratio xcex5 of greater than 6,
the wire is held, during the drawing and between the drawing operations, at a temperature of less than 650xc2x0 C., and preferably less than 600xc2x0 C., without annealing between the drawing passes.
The other characteristics of the invention are:
before the drawing operation, the initial base wire undergoes annealing called overhardening at a temperature of greater than 650xc2x0 C.;
the composition includes less than 5xc3x9710xe2x88x923% of sulfur;
the composition includes from 3% to 4% of copper;
the composition furthermore includes less than 3% of molybdenum;
a wire having a diameter of less than 0.2 mm is drawn;
the drawing is carried out with a deformation ratio xcex5 of greater than 6.6;
the wire furthermore undergoes a brass-plating operation before or between the drawing operations;
the base wire rod having a diameter of greater than 5 mm contains less than 5 oxide inclusions with a thickness of greater than 10 xcexcm over an area of 1000 mm2;
the base wire rod having a diameter of greater than 5 mm contains less than 10 sulfide inclusions with a thickness of greater than 5 xcexcm over an area of 1000 mm2.
The invention likewise relates to the stainless steel used in the process.
The invention also relates to the application of the wire obtained by the process in the tire-reinforcement field.
The description which follows and the appended figures, all given by way of non-limiting example, will make the invention clearly understood.